System variable
maxima_userdirmaxima_userdir names a directory which Maxima searches to find Maxima and Lisp files.
(Maxima searches some other directories as well;
file_search_maxima and file_search_lisp are the complete lists.)
The initial value of maxima_userdir is a subdirectory of the user's home directory,
if Maxima can locate it; otherwise Maxima makes a guess about a suitable directory.
maxima_userdir may be assigned a string which names a directory.
However, assigning to maxima_userdir does not automatically change
file_search_maxima and file_search_lisp;
those variables must be changed separately.